The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 2001-219322, filed on Jul. 19, 2001, the entire contents thereof are hereby incorporated by reference.
1. Field of the Invention
This invention relates to a personal watercraft having an engine with a supercharger incorporated therein. More particularly, the present invention relates to a supply passage of oil to the supercharger for the engine.
2. Description of Background Art
While the power source of most conventional personal watercrafts is a 2-cycle engine, in order to cope with required reductions in pollution, 4-cycle engines have been employed increasingly in recent years. However, since the output power of 4-cycle engine is less than that of a 2-cycle engine of the same total stroke volume, superchargers are often incorporated in 4-cycle engines, in order to make up the power. The assignee of the present application has already proposed a personal watercraft having an engine with a supercharger incorporated therein as Japanese Patent Laid-Open No. 2001-140613.
In this personal watercraft, a 4-cycle engine 2 with a supercharger 3 is incorporated in the inside of a body 1 as shown in prior art FIGS. 11 and 12. The supercharger 3 is disposed on the rear side of the engine 2, and an oil tank 5 is disposed on the front side of the engine 2.
As shown in prior art FIG. 13, an oil pump 4 is provided below the oil tank 5 forwardly of the engine 2, and oil fed under pressure from the oil pump 4 is supplied through a pipe 6d, an oil filter 6 and another pipe 6e to a main gallery 2a of the engine 2. The oil is then supplied to various portions of the engine from the main gallery 2a. 
Oil to a bearing portion 3a of the supercharger 3 is supplied from the main gallery 2a through an oil passage 2d in a lower side bearing portion 2c for a crankshaft 2b, another oil passage 2f in an upper side bearing portion 2e for the crankshaft 2b and a pipe 2g. 
The oil having lubricated the bearing portion 3a of the supercharger 3 passes through a pipe 3b, and is recovered into an oil pan 2i provided at a lower portion of the engine. The oil is further recovered into the oil tank 5 from a pipe 6a through the oil pump 4.
Since the supercharger 3 is disposed on the rear side of the engine 2, and the oil tank 5 is disposed on the front side of the engine 2, the disadvantage of having the oil tank 5 and the oil in the oil tank 5 heated by the supercharger 3 is eliminated.
However, in the prior art described above, an exit 3c of oil having lubricated the bearing portion 3a of the supercharger 3 is disposed lower than an oil surface when the engine is not running. Therefore, after the engine stops, the oil resides in the bearing portion 3a of the supercharger 3. Since the temperature of the supercharger 3 is high immediately after the engine stops, the resident oil is liable to be carbonized. As a result, a problem occurs in that the entire oil supply used for circulation in the engine is liable to be degraded.
The object of the present invention is to provide a personal watercraft having an engine with a supercharger incorporated therein which minimizes the oil residing in the supercharger when the engine is not running, thus reducing the degradation of the entire oil supply. (In the description that follows, the terms xe2x80x9csuperchargerxe2x80x9d and xe2x80x9cturbochargerxe2x80x9d are used interchangeably and have the same meaning).
In order to attain the object above, the present invention is directed to a personal watercraft having an engine with a supercharger incorporated therein, and includes a body formed from a hull and a deck, said engine being provided in said body and said supercharger being provided for said engine, and an oil exit of said supercharger disposed higher than an oil surface when said engine is not running.
Further, according to the present invention, the engine of the personal water craft is a dry sump engine, and an oil tank is provided on an extension line of a crankshaft of said engine.
In addition, the personal watercraft of the present invention also includes a one-way valve interposed in an oil returning passage which communicates with said oil exit of said super charger.
Since the engine is provided in the body formed from the hull and the deck, a supercharger is provided, and the oil exit of the supercharger is disposed higher than the oil surface when the engine is not running, the oil in the supercharger can be discharged quickly from the oil exit. As a result, the oil resident in the supercharger after the engine stops can be minimized, thus reducing the degradation of the entire oil supply.
Also, since the engine of the present invention is a dry sump type engine and the oil tank is provided on an extension line of the crankshaft thereof, the oil surface when the engine is not running can be set low. Thus, oil in the supercharger can be discharged quickly from the oil exit, and as a result, the deterioration of the entire oil is further reduced.
Moreover, since a one-way valve is interposed in the oil returning passage communicating between the oil exit of the supercharger, in a situation when the personal watercraft capsizes, the reverse flow of oil from the oil pan to the high-temperature supercharger can be eliminated. With this configuration, carbonization of oil can be prevented, and degradation of the entire oil supply can be reduced with a higher degree of certainty.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.